10 January, 2023

Audio delay - the unspecified parameter for ham radio transceivers

Elecraft K3: Upper trace is start of sidetone and
lower trace is start of RF ~15 ms later.
An amateur radio transceiver is not a precision measurement device. This is apparent when it comes to measuring time for your own round-the-world signal or when characterizing Long-Delayed Echos (LDE). It won't do to subsitute onset of sidetone for the actual start of transmission of RF. Simililarly there may be an unspecified delay between received RF and start of audio output on the receiver side.  

The main specification for ham radio transceivers is that the sidetone is synchronized with the keying. The delay to start of RF is only of secondary importance. All numbers should be judged against the length of a dot which for instance at a morse code speed of 30 WPM is 40 ms. 

Here are some measurements for the Elecraft K3 and K2 that I did in 2021 for a presentation on LDEs at the HamSci 2021 conference. A video of the presentation is also available: Long delayed radio echoes – the illusive secret of the ionosphere

31 December, 2022

QDX with voltage regulator

Here's my low-band (80m - 20 m) 9 Volt QDX with a voltage regulator. Its only modification is a green rather than a red LED, as I don't like red LEDs to indicate anything but error conditions. 

The power amplifier of the QDX has hardly any built-in protection and can be ruined if run at full power into a poorly matched antenna. It will also easily be ruined if run at a higher voltage than the 9 or 12 Volts one may choose for at build-time.

20 November, 2022

W8BH clock with EU option

The TFT GPS clock with touch control which has been designed by Bruce E. Hall, W8BH, is a very nice clock with a large and easily readable 3.2" color display. Its three different screens have been nicely laid out and designed also. The processor is an STM32 Blue Pill.

I cloned the software and modified it in two simple ways:

1. EU option

This is a backwards compatible version which can be Europeanized with formats for date and units. It also has possibility for removing the display of the battery icon, when running from a USB supply.

New boolean variables to set:

  • US_UNITS - if false: m, kmh, Little-endian date with '.', if true: feet, mph, Middle-Endian date with '/'
  • BATTERY_DISPLAY - true: as original code, false: no display of battery icon and status

03 November, 2022

Planet positions for the Multi Face GPS Clock

Another update, this time to add:

  • Azimuth and elevation for inner and outer planets relative to your present location. The inner planet screen shows Venus and Mercury and alternates also every 10 seconds between showing the position of the sun and the moon. The % illumination is also shown along with an estimate of apparent magnitude
  • The combined local time and UTC display now has an option to show ISO week number, defined to start on Mondays. (It is my understanding that the week number in the US is different, as Sunday is the first day of the week)
  • A new calendar screen now shows Gregorian (western), Julian (eastern) as well as Islamic and Jewish dates. The calculation of the Jewish calendar is tough for the Arduino Mega and takes some 5-6 seconds
  • A screen showing GPS Info has also been included. This screen shows the number of satellites in view (line 0), the number of satellites in use for position fix and their average signal to noise ratio (line 1), the mode and status indicators (line 2), and the Horizontal Dilution of Precision, Hdop, and its characterization in plain text (line 3).

26 August, 2022

QDX on 17 and 15 m: Receiver

I got myself one of the marvellous digital transceivers from QRPLabs recently: The QDX - QRPLabs Digital Transceiver. It is set up with receiver bandpass filters and transmitter lowpass filters for 80, 40, 30, and 20 m. It has also been found that the 40 m filters work well for 60 m. 

The latest firmware, version 1_04, has a new "Band Configuration" screen where one may configure the list of supported bands. It is the intention that higher bands will eventually be supported.

I am not so interested in 80 m, so I wanted to see if I already now could get the receiver to work on 17 m and 15 m. With reference to the schematics, I modified the input filter's inductor, L12. 

07 August, 2022

French, Spanish, German, Icelandic, Swedish, ...

The multi-face Arduino GPS clock is inspired by the Clock Kit from QRPLabs. It is an open source project on GitHub, and it now has support for many more languages in the newly released versjon 1.4.0. As a language nerd myself, I love fiddling with multiple languages and character sets.

The local language option is for display of day name in case local time is shown. The default is English for local time. No matter the choice for local time, English is always used for UTC day name. Here are examples:



23 June, 2022

Reversing the inductor in the Chinese QRP antenna tuner makes all the difference

Like many I was disappointed with the Chinese antenna tuner kit "QRP manual days" back in 2014 and I never really got it to work. 

That was even after I had replaced the two polyvaricon capacitors. The two screws for mounting each of the variable capacitors were too long. The result was that they interfered with the moving plates of the capacitor and I ruined both of them. There was no warning of this in the manual, so beware anyone who buys this kit.

Despite fixing this, it didn't really tune anything. I later learned that it probably works for low bands like 80 m as it is, but I didn't notice that. I thought maybe the toroid core of the inductor was of inferior quality, but never really investigated it, so it sat unused on the shelf for 7-8 years.

14 June, 2022

SV8/LA3ZA part 2

Below is a map showing contacts made from Pythagorio, Samos, early June 2022 using FT8. I tried to contact as many entities (~countries) as possible and got to a total of 55. The main band was 30 m, secondarily 20 m. 40 m and 17 m were also used. 

My quarter-wave antenna @ 30m, shown to the left in the image, performed well, despite the high noise level from the adjacent high-voltage line. The image is in the direction of Turkey (South-East), which is not visible at the time of the image.